1. Field of the Invention
The present invention relates to an optical interconnection module to be a transmitter/receiver in transmitting high-speed optical signals sent and received between chips or boards of a rack and chips or boards of another rack or between chips or boards in a rack such as a data processing apparatus, and an optical-electrical hybrid board that processes optical and electric signals on the board using the same.
2. Description of the Related Arts
In these years, in the field of information and telecommunications, the traffic of information and telecommunications for optically transmitting and receiving large-capacity data at high speed is being improved rapidly. Optical fiber networks are developed for a relatively long distance of a few kilometers or more on the backbone network, metropolitan network, and access network. In future, it is effective to replace signal wiring with optical fibers also for an very short distance such as an inter-rack distance (ranging from a few to a few hundred meters) or intra-rack distance (ranging from a few to a few ten centimeters) of IT equipments such as a router and a server, in order to process large-capacity data without delay.
As for the replacement of inter-rack/intra-rack wiring with optical fibers, in transmission equipments such as a router and a switch, for example, high-frequency signals transmitted from the outside such as Ethernet through optical fibers are inputted to a circuit board called a line card. This line card is formed of a few line cards for a single backplane. The signals inputted to the line cards are aggregate to a circuit board called a switch card through the backplane, processed at an LSI in the inside of the switch card, and outputted to the line cards again through the backplane. Here, in the current equipments, signals at a terabit per second or more are aggregate from the line cards to the switch card through the backplane in the existing conditions. In order to send the signals through the current electric wiring, it is necessary to split the signals into signals at about 1 to 8 gigabits per second for a single wire because of propagation loss. Thus, a hundred wires or more are necessary.
Furthermore, it is necessary to provide an equalizer for these high-frequency lines and to take measures against reflection or crosstalk between wires. In future, if system capacity is increased as in a device that processes information at a terabit per second or more, problems such as the number of wires and the measures against crosstalk become severe more and more in conventional electric wiring. To cope these issues, signal transmission lines between boards of the intra-rack line card through the backplane to the switch card and signal transmission lines between chips in a board are replaced with optical fibers, so that high-frequency signals at 10 gigabits per second or more can be propagated at a low transmission loss. Thus, the replacement of signal transmission lines with optical fibers is promising because the number of wires is small and the measures are unnecessary also for high-frequency signals. In addition to the router and the switch, also in video equipment such as a video camera and consumer electronics such as a personal computer and a mobile telephone, an increase in the speed and capacity of video signal transmission between a monitor and a terminal is demanded as well as problems of taking measures against signal delay and noise become noticeable in conventional electric wiring, for future high-definition images. Thus, the replacement of signal transmission lines with optical fibers is effective.
In order to implement such a high-speed optical interconnection circuit and to apply the circuit to inter-rack/intra-rack transmission, an optical module and a circuit are necessary, which are excellent in performance, downsizing, integration, and component packaging properties with inexpensive fabrication instruments. Therefore, a downsized, high-speed optical module is proposed in which an optical waveguide is used for a wiring medium, which is more inexpensive than a conventional optical fiber and advantageous in densification, and optical components and the optical waveguide are integrated on a substrate. As for the interconnection transmission rate, it is expected that high-speed modules operating at 25 gigabits per second/ch or 40 gigabits per second/ch will be necessary in future, from optical modules currently operating based on 10 gigabits per second/ch. Concerning this, the mainstream of optical sources directed to optical interconnection modules is direct modulation currently represented by surface emitting lasers (Vertical-Cavity Surface-Emitting Laser: VCSEL) or the like. However, since it is expected that a transmission rate of 25 gigabits per second/ch or more described above is a limit of direct modulation, it can be considered that an optical module using an optical source according to external modulation will be one of approaches for increasing speed in future.
As for a conventional method for the optical interconnection module, Japanese Patent Application Laid-Open Publication No. 2008-294226 discloses a form of mounting an optical interconnection module in which an optical module having a laser diode array, a photo diode array, and an integrated circuit integrated thereon is mounted on an optical waveguide wiring board with solder bumps. In this example, in mounting the optical module on the optical waveguide wiring board, the laser diode array or the photo diode array and an optical waveguide are optically connected to each other in the vertical direction of the substrate, and at the same time, the optical module and the optical waveguide wiring board are electrically connected to each other.